The invention relates to a printing device for printing markings onto the covering of an insulated wire.
A plurality of different wires are used as connecting elements between structural elements or assemblies in electrical and electronic control systems. These wires are generally provided with an outer insulation made of plastic material. A plurality of the wires are insulated round wires with cross-sections selected in accordance with the current density and therefore with different diameters. The insulation is configured in different colours to optically divide into corresponding groups of the set.
It is additionally necessary to provide each individual wire with its own marking at both wire ends. These markings are usually defined in the design documents by the producer of the control system and enable fault-free and simple handling for production and further service. Depending on the number of control systems or devices produced, the wires are identified by means of appropriate organization forms and marking devices before wiring into the device. For regular production, complete sets of wires for assemblies or also for complete systems are created using an automatic marking and bundling technique. For this, the data are processed and prepared by means of electronic data processing using the design documents.
Automatic marking systems use technically complex inkjet printers using ink containing solvent for marking or printing. The inscription is applied partially around the surface of the wire.
A simpler method of marking used for smaller production quantities is to glue a self-adhesive label to the wire. The labels are printed on using standard thermal transfer printers and are then wound and glued around the wire.
In addition, the use of narrow thin plastic tags with two holes provided at the ends is known. These plastic tags are inscribed with the marking, e.g. by means of thermal transfer printing or written by hand. The wire is directed through the two holes one after the other, and the tag is thus fastened to the wire with the text outside.
It is additionally known to mark round wires by attaching tubes that are already preprinted with a letter or with a number or also laterally slotted tubes. In this method a plurality of individual tubes must be attached in succession on the wire to display the marking. Tubes with different diameters are used to correspond to the respective wire diameter.
A similar solution to this is to attach shrink tubing pieces to the wire. This marking method has the essential advantage over the use of individual tubes that each have one letter that the shrink tubing end can already be provided with the complete marking. The shrink tubing is printed on using a thermal transfer printer in a known manner.
All the specified marking processes, with the exception of the complex inkjet printing, do not print directly onto the wire insulation, but use an additional object that has an inscription and is then fastened to the wire in a suitable manner.
A further known printing process that enables direct printing onto the wire insulation uses punches and operates substantially using a hot stamping process. Stamping wheels adapted to the wire diameter and having preformed letters or numbers are inserted into the punches. Several stamping wheels are arranged on one punch and can be respectively adjusted by rotating so that a multiple-digit marking is created. The stamping wheels are heated to a correspondingly high temperature. When the punch is closed, the stamping wheels come into contact with the round wire to be printed on and transfer their contour directly onto the wire surface in colour by means of a standard hot stamping foil. The advantage with this technology is that the insulated wire surface is printed on directly. However, the handling is very complex because of the mechanical adjustment of each individual stamping wheel for each individual mark. Moreover, each stamping wheel has a fixed mark size and only a small and limited range of marks.
It is evident from the listed printing processes for printing on round wires that standard known printing techniques with their ease of printing cannot be used because of the round shape of the surface of the wires, since their application requires flat printing surfaces.